In communications networks, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed.
For example, future generations of cellular communications networks are expected to provide high data rates, up to several Giga bits per second (Gbps) whilst at the same time be energy efficient. One way to achieve such high data rates and/or to lower the energy consumption in cellular communications networks is to deploy reconfigurable antenna systems (RAS). In general terms, a RAS can be defined as an antenna system whose radiation characteristics can be changed by a network node in the communications networks after deployment and be adapted to, e.g., current traffic needs. For example, the antenna system can be reconfigured to better serve a traffic hotspot by, e.g., increasing the antenna gain toward the hotspot location. To efficiently use RAS it has to be automatically controlled, for example by using a self-organizing network (SON) mechanism. In reality the traffic distribution in many communications networks changes during the day, typically in predefined patterns. For example during office hours in weekdays most of the traffic is in office buildings and during the evenings most traffic is in residential buildings. Therefore it would be favorable to have different RAS settings for different time periods and to toggle between the RAS settings depending on the current traffic distribution.
The cell re-selection as define in the Long Term Evolution (LTE) family of telecommunications standards for wireless devices in radio resource control (RRC) idle mode is mainly based on the signal strength of Common Reference Signals (CRS) denoted CRS0 and CRS1. In short, the wireless devices measures received power of CRS from multiple radio access network nodes and choose the radio access network node(s) corresponding to the CRS with highest received power. If multiple antenna ports are used the cell re-selection of the wireless device could be based on the highest received signal strength of the CRS. The wireless devices may select to report only CRS0, i.e. the use of CRS1 can be optional and implementation dependent even in the case when multiple antenna ports are used by the radio access network nodes. For legacy wireless devices (supporting LTE up to Release 8 or 9), the CRSs (up to 4 CRSs) are also used at the wireless devices for determining a precoding matrix, rank and modulation and coding scheme for downlink data transmission.
Radio access network nodes can configure a wireless device in radio resource RRC connected mode to perform reference signal received power (RSRP) measurements from its serving radio access network node as well as searching and finding the strongest neighboring radio access network node(s). For example, the wireless devices can perform RSRP measurement every 40 ms for non-discontinuous reception (non-DRX) and during on-duration for discontinuous reception (DRX) cases. Furthermore, each wireless device can be capable of tracking 8 strongest cells simultaneously if the signal to interference plus noise ratio (SINR) is high enough, as described in further detail in 3GPP TS 36.133 version 8.2.0 Release 8.
Instantly switching the coverage areas of multiple radio access network nodes could lead to dropped calls and bad user experience for served wireless devices. One reason for this is that active wireless devices do not have a sufficient amount of time to perform handover from the currently serving radio access network node to the target serving radio access network node. This can lead to an increased probability for radio link failure (RLF). After a RLF the wireless device can try to connect to the network again by sending an RRCConnectionReestablishment request message to its serving radio access network node. However, if the serving radio access network node does not have the UE context (where UE is short for User Equipment, denoting the wireless device), the wireless device moves to RRC idle mode and the connection will be lost. The wireless device context is established at a radio access network node when the transition to RRC connected mode is completed for a wireless device or in the target radio access network node after completion of handover. Further, slowly changing the RAS setting for the respective cells in a random way from the current RAS settings to the new RAS setting can lead to unnecessary handovers during the switch and temporary coverage holes which, again, can lead to dropped users.
Hence, there is still a need for an improved handling of handovers in communications networks using RAS.